This study proposes to test the efficacy of an ecodevelopmental, parent-centered drug abuse and HIV prevention intervention for Hispanic, behavior problem adolescents and their families (Familias Unidas; United Families). Familias Unidas targets three risk and protective factors for behavior problems, drug abuse and risky sexual behavior: family functioning, parental monitoring, and the adolescents' social cognitive mediators regarding drugs and sex. An indicated sample of 240 behavior problem adolescents attending 8th grade and their primary parent figure will be assessed at Baseline, and at 6-, 18-, and 30- months. Participants will be randomized after baseline into one of two conditions, Familias Unidas or Community Control. Familias Unidas has previously been tested to examine the impact on risk and protective factors for adolescent drug use and HIV in selected samples of Hispanic immigrant adolescents and their families. In the first of two studies, Familias Unidas was shown to be efficacious relative to a no-intervention control condition in increasing parental investment and in reducing adolescent behavior problems. In the second study, Familias Unidas showed promise relative to two attention control conditions in reducing behavior problems and preventing drug use and risky sexual behavior among behavior problem adolescents. Hierarchical Linear Modeling (HLM) will be used to test (H1) the efficacy of Familias Unidas in reducing adolescent behavior problems over time; (H2) the efficacy of Familias Unidas in preventing adolescent drug use over time; and (H3) the efficacy of Familias Unidas in preventing adolescent risky sexual behaviors over time. Additionally HLM will be used to determine whether (H1a) the effect of Familias Unidas on adolescent behavior problems will be mediated by family functioning; (H2a) the effect of Familias Unidas on drug use will be partially mediated by: a) adolescent behavior problems, b) parental monitoring of peers, c) peer behavior problems defined as peer drug use, and d) adolescent social cognitive mediators regarding drugs; and (H3a) the effect of Familias Unidas on risky sexual behavior will be partially mediated by: a) adolescent drug use, b) parental monitoring of peers, c) peer behavior problems defined as peer sexual behavior, and d) adolescent social cognitive mediators regarding sex.